The Institute of Electrical and Electronics Engineers (IEEE) has adopted a set of standards for wireless local area networks (LANs), known as 802.11. Wireless products satisfying 802.11a, 802.11b, and 802.11g, as well as 802.16, are currently on the market, for example.
Recently, an 802.11n standard, known also as the Enhancement for High Throughput wireless standard, has emerged. Under the 802.11n standard, transmitters and receivers each have multiple antennas for transmission and reception of data. As a multiple input, multiple output (MIMO) technology, 802.11n is designed to coordinate multiple simultaneous radio signals, and is expected to support a bandwidth of greater than 100 megabits per second (Mbps). An 802.16m standard has been initiated, which supports the International Telecommunication Union (ITU) IMT-ADVANCE (also known as “4G”). Advanced MIMO is essential technology to fulfill the target requirement of IMT-ADVANCE.
Single-user MIMO, or SU-MIMO, involves communications between a single base station (BS) and a mobile station (MS) or subscriber station (SS). Multiple-user MIMO, or MU-MIMO, is concerned with communication between the BS and multiple MSs or SSs. During the uplink, multiple MSs transmit data to the BS; during the downlink, the BS transmits signals to multiple MSs in a single resource block. MU-MIMO may benefit from both multi-user diversity and spatial diversity, and can obtain higher throughput than the SU-MIMO system.